Chemical Engineering | GASIFICATION
Nexterra
Process flow illustrationof the CHP gasification system with the GE Jenbacherengineat The University of British Columbia.
of interest in gasification is driven by several key concerns: the need to reduce carbon dioxide (CO2) emissions and the rising demand for cleaner burning fuels which produce fewer secondary pollutants like nitrogen oxides (NOx) and sulfur oxides (SOx). A third factor is the growing energy demand among developing countries for liquid and gaseous fuel. In China, for example, oil is in short supply, but coal is abundant. Gasifying this coal creates a number of advantages over burning it directly. At its core, gasification is the process of reacting carbon-based fuels at high temperatures and low oxygen to create synthesis gas, also known as syngas, a mixture of mainly carbon monoxide and hydrogen. After being cleaned up, syngas can be fired into a conventional
gas burner or an internal combustion engine. According to Grace, this can lead to greater efficiency than burning solid particles from coal or wood. The cleanup step cuts down on the emissions of secondary pollutants derived from impurities in the original wood or coal. Another option is that that instead of being burned, syngas can also be converted to larger molecules via the Fisher-Tropsch process, creating liquid fuels or commodity chemicals like methanol, ethanol and alkanes. Today, gasification is considered to be one of most versatile and efficient ways to convert low-cost wood waste and other biomass fuels into thermal energy or electricity. It is also a key technology in helping to achieve global greenhouse gas-emission reduction objectives, says Grace, who is chair of the 3rd International Symposium on Gasification, held in conjunction with the 62nd Canadian Chemical Engineering Conference Oct 14-17 in Vancouver. “Our dependence on fossil fuels is still so great that we must find ways to decarbonize them and reduce emissions associated with their usage,” Grace says. He points to global trends indicating rising fossil-fuel consumption due to improved living standards in developing nations, increasing populations, as well as the West’s reluctance to trim its prodigious energy appetite. “We need to manage our carbon better and find alternatives — preferably renewable energy resources.” Grace’s scholarship includes the study of fluidized bed gasification, a technology dating back to the 1920s. Along with a UBC team that includes Tony Bi, Naoko Ellis, Jim Lim and Paul Watkinson, Grace is seeking fluidized bed reactors that can do more with less. One example is a dual fluidized bed steam gasification system. Most gasifiers contact fuel with a sub-stoichiometric amount of air, which is mostly nitrogen. The inert nitrogen dilutes the final gas stream, decreasing its calorific value. Replacing the air with steam leads to a better final product,
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